Abstract submissions include abstracts only and announcements.  In the last year there have only been 2 of these abstract-only submissions.

A possibly better measure is a count of pdf files (there are some submissions which only have html or only ps)

A picture of the total:

And of the last two years:

For 2011, predictions can be anywhere from 6,000 (linear on last two years) to about 18,500 (exponential on last two years)
(x in the equations is days, so the exponential has a growth rate of .0007 per day, while the linear is 1.35 papers per day)

Usage statistics, for whatever they are worth.  NOTE: Paper downloads are contained in the LogEc data.